Heinrich Hertz observes the photoelectric effect

Background. Heinrich Hertz, a German physicist, became a full professor at the University of Karlsruhe in 1885. He conducted landmark research into electromagnetic waves, aiming to prove Maxwell's predictions. His experiments involved discharging Leyden jars into Riess spirals, observing sparks in distant coils, which established the existence of airborne electromagnetic waves.

Observation. In 1887, Hertz observed the photoelectric effect, noting that ultraviolet light caused electrons to be emitted from materials. This observation occurred during his work on the production and reception of electromagnetic waves. The phenomenon was studied to infer properties of atoms and solids, influencing the concept of wave-particle duality.

Apparatus. Hertz's receiver consisted of a coil with a spark gap, where sparks were seen upon detecting electromagnetic waves. The energy barrier to photoemission was often increased by oxide layers, so practical experiments used clean metal surfaces in evacuated tubes. This setup allowed for the observation of photoelectric fatigue on fresh metallic surfaces.